Solid-state imaging element and electronic device

ABSTRACT

A solid-state imaging element of the present disclosure has arranged inside a pixel: a charge accumulation unit that accumulates a charge photoelectrically converted by a photoelectric conversion unit; a reset transistor that selectively applies a reset voltage to the charge accumulation unit; an amplification transistor having a gate electrode being electrically connected to the charge accumulation unit; and a selection transistor connected in series to the amplification transistor. Additionally, the solid-state imaging element includes: first wiring electrically connecting the charge accumulation unit and the gate electrode of the amplification transistor; second wiring electrically connected to a common connection node of the amplification transistor and the selection transistor and formed along the first wiring; and third wiring electrically connecting the amplification transistor and the selection transistor.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 17/073898, filed Oct. 19, 2020, which is acontinuation application of U.S. patent application Ser. No. 16/349035,filed on May 10, 2019, which is U.S. National Phase of InternationalPatent Application No. PCT/JP2017/040942 filed on Nov. 14, 2017, whichclaims priority benefit of Japanese Patent Application No. JP2016-239152 filed in the Japan Patent Office on Dec. 9, 2016, Each ofthe above-referenced applications is hereby incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a solid-state imaging element and anelectronic device.

BACKGROUND ART

In a complementary metal oxide semiconductor (CMOS) image sensor, oneexample of a solid-state imaging element, a floating diffusion unit(hereinafter, referred to as a “FD unit”) is in a floating state when areset pulse is returned to an inactive state after FD unit has beenreset. Therefore, feedthrough corresponding to capacitive couplinglowers a voltage of the FD unit.

Furthermore, when the reset pulse is returned to the inactive state,charge injection, that is, a phenomenon in which electrons existing in achannel of a reset transistor are injected into the FD unit also occurs,and this phenomenon also lowers the voltage of the FD unit (hereinafterreferred to as “FD voltage”) in a similar manner. The FD voltage dropwould deteriorate readout of electrons from a photoelectric conversionunit, and therefore, there is a need to perform pixel design inconsideration of the amount of drop in the FD voltage.

As a pixel design in consideration of the FD voltage drop, it isconceivable to enhance routing of wiring within a pixel and use couplingaccompanying a potential change of the wiring. Conventionally, as atechnique to enhance routing of wiring within a pixel, there is atechnique in which shield wiring is provided below the FD wiring and theshield wiring is conductively connected to an output terminal of asource follower amplifier (refer to Patent Document 1, for example).

CITATION LIST Patent Document

Patent Document 1: Japanese Patent Application National Publication(Laid-Open) No. -69

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Meanwhile, in a typical CMOS image sensor, merely the feedthrough of thereset pulse and the charge injection in the reset transistor hasinfluence of the voltage drop after resetting of the FD unit, and thesignal charge stays in the FD unit for several microseconds.Accordingly, the FD unit is not easily influenced by electric field darkcurrent such as junction leakage.

On the other hand, in a case where the charge accumulation unit cannotbe depleted, for example, in a case where an organic photoelectricconversion film is used in a photoelectric conversion unit and one ofthe accompanying electrodes is connected to the FD unit, it is necessaryto accumulate a signal charge in the FD unit. Therefore, the darkcurrent of the FD unit is also accumulated together with accumulation ofthe signal charge. Furthermore, in the configuration using an organicfilm, a time interval of correlated double sampling (CDS) processing ofthe signals before and after accumulation is equal to the signalaccumulation time. Therefore, after readout of the level beforeaccumulation, the selection pulse is turned into an inactive state andenters a long accumulation phase.

Meanwhile, in a case where the signal charge is accumulated in the FDunit, the FD unit can be reset with GND in order to reduce the darkcurrent. This can reduce a voltage difference between the voltage of theFD unit and voltage of the semiconductor substrate in the dark conditionand weaken the electric field, enabling reduction of the dark current.However, in addition to the feedthrough by the reset pulse and thechannel charge injection in the reset transistor as described above, thefeedthrough due to the selection pulse lowers the FD voltage as well.This causes a voltage difference between the FD unit and thesemiconductor substrate, and the electric field generated by this wouldincrease the dark current in the FD unit. In order to avoid theinfluence of these feedthrough and channel charge injection, it isconceivable to adjust the reset voltage in consideration of thefeedthrough amount. However, it is necessary to consider the influenceof an increase in cost and power consumption to be caused by an increasein bias voltage and the number of power supply units, for example.

According to the above-described conventional technique described inPatent Document 1, shielding the FD wiring by the shield wiring biasedwith the output of the source follower amplifier can increase a voltagecharge conversion ratio. However, the conventional technique describedin Patent Document 1 has not taken into consideration avoidance of theinfluence of the feedthrough due to the reset pulse, the channel chargeinjection in the reset transistor, nor the feedthrough due to theselection pulse.

The present disclosure aims to provide a solid-state imaging element andan electronic device capable of avoiding the influence of feedthrough bythe reset pulse, channel charge injection in a reset transistor, andfeedthrough due to a selection pulse.

Solutions to Problems

According to an embodiment of the present disclosure, a solid-stateimaging element having arranged inside a pixel:

a charge accumulation unit that accumulates a charge photoelectricallyconverted by a photoelectric conversion unit; a reset transistor thatselectively applies a reset voltage to the charge accumulation unit; anamplification transistor having a gate electrode being electricallyconnected to the charge accumulation unit; and a selection transistorconnected in series to the amplification transistor, the solid-stateimaging element including: first wiring electrically connecting thecharge accumulation unit and the gate electrode of the amplificationtransistor; second wiring electrically connected to a common connectionnode of the amplification transistor and the selection transistor andformed along the first wiring; and third wiring electrically connectingthe amplification transistor and the selection transistor. Moreover, anelectronic device provided for achieving the above-described purposeaccording to the present disclosure includes a solid-state imagingelement having the above-described configuration.

In the solid-state imaging element having the above-describedconfiguration or the electronic device including the solid-state imagingelement, since the second wiring is formed along the first wiring, it ispossible to increase capacitive coupling between the first wiring andthe second wiring via parasitic capacitance. Moreover, since the secondwiring is connected to the common connection node of the amplificationtransistor and the selection transistor, it is possible to boost an FDvoltage by the capacitive coupling between the first wiring and thesecond wiring, enabling adjustment of voltage of the charge accumulationunit to an appropriate value. Furthermore, since the amplificationtransistor and the selection transistor are connected to each other bythe third wiring rather than by sharing a diffusion layer, the degree offreedom of the layout of the selection transistor is increased. Inaddition, since the selection transistor is disposed at a positiondistant from the charge accumulation unit, it is possible to suppress avoltage drop of the charge accumulation unit due to the influence of thefeedthrough due to the selection pulse, as compared with the case wherethe diffusion layer is shared.

Effects of the Invention

According to the present disclosure, it is possible to avoid influenceof a feedthrough by a reset pulse, channel charge injection in a resettransistor, and a feedthrough due to a selection pulse, enablingadjustment of the voltage of the charge accumulation unit to anappropriate value.

Note that effects described herein are non-limiting. The effects may beany effects described in the present description. Note that effectsdescribed herein are provided for purposes of exemplary illustration andare not intended to be limiting. Still other additional effects may alsobe contemplated.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a system configuration diagram illustrating a basicconfiguration of a solid-state imaging element to which the technologyof the present disclosure is applied.

FIGS. 2A and 2B are circuit diagrams illustrating a circuitconfiguration example of a pixel using an organic photoelectricconversion film as a photoelectric conversion unit.

FIG. 3 is a timing waveform diagram illustrating a timing relationshipof pixel drive in a typical CMOS image sensor.

FIG. 4 is a timing waveform diagram illustrating a timing relationshipof pixel drive in a case where charges are accumulated in an FD unitusing an organic photoelectric conversion film in a photoelectricconversion unit.

FIGS. 5A and 5B are view illustrating a factor of lowering the voltageof the floating diffusion unit and an action of boosting the voltage.

FIG. 6A is a plan view schematically illustrating a wiring structureaccording to Example 1. FIG. 6B is a cross-sectional view taken alongline A-A of FIG. 6A.

FIG. 7A is a plan view schematically illustrating a wiring structureaccording to Example 2. FIG. 7B is a cross-sectional view taken alongline B-B of FIG. 7A.

FIG. 8A is a plan view schematically illustrating a wiring structureaccording to Example 3. FIG. 8B is a cross-sectional view taken alongline C-C of FIG. 8A.

FIG. 9 is a cross-sectional view illustrating an example of a verticalspectroscopic pixel structure.

FIG. 10 is a block diagram illustrating a configuration of an imagingapparatus as an example of an electronic device of the presentdisclosure.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the technology of the present disclosure(hereinafter, embodiment(s)) will be described in detail with referenceto the drawings. The technology of the present disclosure is not limitedto the embodiments, and various materials, or the like, of theembodiment are examples. In the following description, the same elementsor elements having the same function will be denoted by the samereference symbols, and duplicated description will be omitted. Note thatdescription will be presented in the following order.

-   1. General description related to solid-state imaging element,    signal processing circuit, and electronic device of the present    disclosure-   2. Solid-state imaging element to which technology of the present    disclosure is applied-   2-1. Basic system configuration-   2-2. Pixel circuit (example using organic photoelectric conversion    film in photoelectric conversion unit)-   2-3. Voltage drop in floating diffusion unit-   3. Embodiments of the present disclosure-   3-1. Example 1 (example in which first wiring and second wiring are    stacked in different layers)-   3-2. Example 2 (example in which first wiring and second wiring are    arranged in parallel in same layer)-   3-3. Example 3 (example in which first wiring and second wiring are    arranged in parallel in different layers)-   3-4. Example 4 (example of wiring material of first wiring, second    wiring, and third wiring)-   4. Vertical spectroscopic pixel structure-   5. Electronic device according to the present disclosure (example of    imaging apparatus)-   6. Configuration applicable by the present disclosure

<General Description Related to Solid-State Imaging Element andElectronic Device of the Present Disclosure>

In a solid-state imaging element and an electronic device of the presentdisclosure, it is possible to have a configuration in which a resetvoltage is at a GND level when a charge accumulation unit accumulatesholes, or in which the reset voltage is either a power supply voltage ora boosted voltage having a voltage value higher than the power supplyvoltage when the charge accumulation unit accumulates electrons.

In the solid-state imaging element and the electronic device of thepresent disclosure including the preferable configuration describedabove, it is possible to have a configuration in which the first wiringand the second wiring are formed in parallel in different wiring layers,or formed in parallel in a same wiring layer. Furthermore, it ispossible to have a configuration in which any one of the first wiring,the second wiring, and the third wiring includes a wiring materialdifferent from the other wiring.

Furthermore, in the solid-state imaging element and the electronicdevice of the present disclosure including the preferable configurationdescribed above, it is possible to have a vertical spectroscopic pixelstructure in which at least two photoelectric conversion regions arestacked in a light incident direction in a semiconductor substrate onwhich pixels are formed. Furthermore, it is possible to adopt aconfiguration having a back-illuminated pixel structure.

<Solid-State Imaging Element to which Technology of the PresentDisclosure is Applied>

The solid-state imaging element to which the technology of the presentdisclosure is applied will be described with reference to FIG. 1 . FIG.1 is a system configuration diagram illustrating a basic configurationof the solid-state imaging element to which the technology of thepresent disclosure is applied. Here, the solid-state imaging elementaccording to the present application example will be described using anexample of a CMOS image sensor which is one type of a solid-stateimaging element of the X-Y address system.

[Basic System Configuration]

A solid-state imaging element 10 according to the present applicationexample includes: a pixel array unit 11 formed on a semiconductorsubstrate (semiconductor chip) (not illustrated); and a peripheralcircuit unit integrated on the semiconductor substrate same as thesubstrate including the pixel array unit 11. The peripheral circuit unitincludes, for example, a vertical drive unit 12, a column processingunit 13, a horizontal drive unit 14, and a system control unit 15.

The solid-state imaging element 10 further includes a signal processingunit 18 and a data storage unit 19. The signal processing unit 18 andthe data storage unit 19 may be mounted on the same substrate as thesolid-state imaging element 10, or may be arranged on a substrateseparate from the solid-state imaging element 10. Furthermore,processing of each of the signal processing unit 18 and the data storageunit 19 may be performed by an external signal processing unit providedon a substrate different from the solid-state imaging element 10, forexample, by a digital signal processor (DSP) circuit or by software.

The pixel array unit 11 has a configuration including an array of pixels(unit pixel) 20 including a photoelectric conversion unit that performsphotoelectric conversion and generates and accumulates photo-chargecorresponding to the amount of received incident light, arranged in arow direction and a column direction, that is, two-dimensionallyarranged in a matrix. Here, the row direction refers to a pixelarrangement direction in pixel rows (that is, a horizontal direction),while the column direction refers to a pixel arrangement direction inpixel columns (that is, a vertical direction).

With respect to the matrix of pixel arrangements in the pixel array unit11, pixel drive lines 16 (16 ₁ to 16 _(m)) are wired in the rowdirection for each of pixel rows, while vertical signal lines 17 (17 ₁to 17 _(n)) are wired in the column direction for each of pixel columns.The pixel drive line 16 transmits a drive signal output from thevertical drive unit 12 when driving the pixel 20. Although FIG. 1illustrates a case where the pixel drive line 16 has a single wire, thenumber of wires is not limited to one. One end of the pixel drive line16 is connected to an output terminal corresponding to each of rows ofthe vertical drive unit 12.

The vertical drive unit 12 includes a shift register, an addressdecoder, and the like, and drives each of the pixels 20 of the pixelarray unit 11 simultaneously for all the pixels, or in units of rows,etc. That is, the vertical drive unit 12, together with the systemcontrol unit 15 that controls the vertical drive unit 12, has aconfiguration as a drive unit that drives each of the pixels 20 of thepixel array unit 11. Although illustration of a specific configurationis omitted, the vertical drive unit 12 has a configuration having twoscanning systems, namely, a readout scanning system and a sweep scanningsystem, in typical cases.

The readout scanning system sequentially selects and scans the pixels 20of the pixel array unit 11 in units of rows in order to read out signalsfrom the pixels 20. The signal read out from the pixel 20 is an analogsignal. The sweep scanning system applies sweep scanning ahead of thereadout scanning by the time corresponding to the shutter speed onto thereadout rows on which the readout scanning is performed by the readoutscanning system.

Sweep scanning by the sweep scanning system is performed to sweep outunnecessary charges from the photoelectric conversion unit of the pixel20 in the readout rows, whereby the photoelectric conversion unit isreset. Moreover, sweeping out (resetting) unnecessary charges by thissweep scanning system leads to electronic shutter operation. Here, theelectronic shutter operation refers to operation of discardingphoto-charge of the photoelectric conversion unit and starting a newexposure (start accumulation of photo-charge).

The signal read out by the readout operation by the readout scanningsystem corresponds to the amount of light received after the readoutoperation or the electronic shutter operation just before the readoutoperation. Moreover, the period from the readout timing by theimmediately preceding readout operation or the sweep timing by theelectronic shutter operation to the readout timing by the presentreadout operation is an exposure period of the photo-charge in the pixel20.

The signal output from each of pixels 20 of the pixel row selectivelyscanned by the vertical drive unit 12 is input to the column processingunit 13 through each of the vertical signal lines 17 for each of pixelcolumns. For each of pixel columns of the pixel array unit 11, thecolumn processing unit 13 performs predetermined signal processing on asignal output from each of pixels 20 of the selected row through thevertical signal line 17, and together with this, temporarily storespixel signals after the signal processing.

Specifically, the column processing unit 13 performs signal processingat least including noise removal processing such as correlated doublesampling (CDS) processing or double data sampling (DDS) processing. Forexample, the CDS processing is effective for removing pixel-specificfixed pattern noise such as reset noise and threshold variation of theamplification transistor in the pixel 20. In addition to the noiseremoval processing, the column processing unit 13 may include ananalog-to-digital (AD) conversion function, and an analog pixel signalcan be converted into a digital signal and output, for example.

The horizontal drive unit 14 includes a shift register, an addressdecoder, or the like, and sequentially selects unit circuitscorresponding to the pixel columns of the column processing unit 13.Along with the selective scanning by the horizontal drive unit 14, thecolumn processing unit 13 sequentially outputs pixel signals subjectedto signal processing for each of unit circuits.

The system control unit 15 includes a timing generator that generatesvarious timing signals and the like, and controls driving of thevertical drive unit 12, the column processing unit 13, and thehorizontal drive unit 14, or the like on the basis of various timinggenerated by the timing generator.

The signal processing unit 18 includes at least an arithmetic processingfunction and performs various signal processing such as arithmeticprocessing on the pixel signal output from the column processing unit13. The signal processing unit 18 is an example of the signal processingcircuit of the present disclosure, and its details will be describedlater. The data storage unit 19 temporarily stores data necessary forsignal processing in the signal processing unit 18.

Note that the above-described system configuration is merely an example,and the present invention is not limited to this configuration. Forexample, it is allowable to have a system configuration in which thedata storage unit 19 is arranged downstream of the column processingunit 13 and pixel signals output from the column processing unit 13 aresupplied to the signal processing unit 18 via the data storage unit 19.Alternatively, it is allowable to have a system configuration in whichthe column processing unit 13 includes an AD conversion function ofperforming AD conversion for each of columns or a plurality of columnsof the pixel array unit 11, and in which the data storage unit 19 andthe signal processing unit 18 are installed in parallel with respect tothe column processing unit 13.

The solid-state imaging element 10 to which the technology of thepresent disclosure is applied can have a structure in which constituentssuch as the column processing unit 13, the signal processing unit 18, orthe data storage unit 19 are mounted on a same semiconductor substratetogether with the pixel array unit 11, that is, a lay-flat structure.Alternatively, it would be possible to have a structure in whichconstituents such as the column processing unit 13, the signalprocessing unit 18, or the data storage unit 19, are dispersedly mountedon one or more other semiconductor substrates different from thesemiconductor substrate on which the pixel array unit 11 is mounted, andthese semiconductor substrates are stacked, namely, possible to have astacked structure.

Furthermore, the pixel structure can either be a back-illuminated pixelstructure or a surface-illumined pixel structure. Here, the“back-illuminated pixel structure” represents a pixel structure thatcaptures incident light (light is emitted) from a substrate back side(backside of semiconductor substrate), that is, opposite to thesubstrate front side in which wiring layer of the semiconductorsubstrate is formed. In contrast, the “front-illuminated pixelstructure” refers to a pixel structure that captures incident light(light is emitted) from the substrate front side.

[Pixel Circuit]

Here, the following is an example of the pixel 20 having a pixel circuitin which an organic photoelectric conversion film is used in thephotoelectric conversion unit. FIGS. 2A and 2B are circuit diagramsillustrating a circuit configuration example of the pixel 20 using anorganic photoelectric conversion film in a photoelectric conversionunit. The pixel 20 according to the present configuration exampleincludes a reset transistor 22, an amplification transistor 23, and aselection transistor 24 in addition to a photoelectric conversion unit21.

Here, each of the reset transistor 22, the amplification transistor 23,and the selection transistor 24 uses an N channel MOS transistor, forexample. However, the combination of the conductivity types of the resettransistor 22, the amplification transistor 23, and the selectiontransistor 24 exemplified here is merely an example, and the combinationis not limited to this example.

The photoelectric conversion unit 21 includes an organic photoelectricconversion film 211. The organic photoelectric conversion film 211 issandwiched between an upper electrode 212 and a lower electrode 213. Inthis photoelectric conversion unit 21, at least the lower electrode 213is divided for each of pixels. The lower electrode 213 is electricallyconnected to a floating diffusion unit (FD unit) 25. The FD unit 25serves as a charge accumulation unit/charge voltage conversion unitconfigured to accumulate charges and convert the accumulated chargesinto voltage. A bias voltage is applied to the upper electrode 212 by abias power supply 26.

The reset transistor 22 has one source/drain electrode connected to theground (GND), for example, and has the other source/drain electrodeconnected to the FD unit 25. To a gate electrode of the reset transistor22, a reset pulse RST having high level being active is given from thevertical drive unit 12 illustrated in FIG. 1 . The reset transistor 22turns to a conducting state in response to the reset pulse RST and then,discards the charge of the FD unit 25 to GND and thereby resets the FDunit 25.

The amplification transistor 23 has the gate electrode connected to theFD unit 25 and has one source/drain electrode connected to a pixel powersupply VAMP (for example, a power supply line of the power supplyvoltage V_(DD)). The amplification transistor 23 serves as an input partof a source follower that reads out a signal obtained by photoelectricconversion by the photoelectric conversion unit 21. That is, theamplification transistor 23 has the other source/drain electrodeconnected to the vertical signal line 17 via the selection transistor24, thereby constituting a current source (not illustrated) and a sourcefollower connected to one end of the vertical signal line 17.

The selection transistor 24 is connected in series with theamplification transistor 23 between the pixel power supply VAMP and thevertical signal line 17. Specifically, for example, one source/drainelectrode of the selection transistor 24 is connected to the othersource/drain electrode of the amplification transistor 23, while theother source/drain electrode is connected to the vertical signal line17. To the gate electrode of the selection transistor 24, a selectionpulse SEL having high level being active is given from the verticaldrive unit 12. The selection transistor 24 is turned to a conductionstate in response to the selection pulse SEL and thereby relays a signaloutput from the amplification transistor 23 to the vertical signal line17 with the pixel 20 in a selected state.

In the pixel 20 having the above-described configuration, chargesphotoelectrically converted by the organic photoelectric conversion film211 of the photoelectric conversion unit 21 are accumulated in the FDunit 25. Here, depending on the polarity of the bias voltage appliedfrom the bias power supply 26 to the upper electrode 212, the chargesaccumulated in the FD unit 25 can either be electrons or holes.

Specifically, as illustrated in FIG. 2A, in a case where the polarity ofthe bias voltage applied to the upper electrode 212 by the bias powersupply 26 is positive, the holes move to the lower electrode 213 and arethen accumulated in the FD unit 25, while electrons move to the upperelectrode 212, out of the charges generated in the organic photoelectricconversion film 211. In this case, in order to reset the FD unit 25 inwhich holes are accumulated, a reset voltage V_(rst) at the time whenthe FD unit 25 is reset by the reset transistor 22 is set to the GNDlevel as illustrated in FIG. 2A.

In contrast, as illustrated in FIG. 2B, in a case where the polarity ofthe bias voltage applied to the upper electrode 212 by the bias powersupply 26 is negative, the electrons move to the lower electrode 213 andare then accumulated in the FD unit 25, while holes move to the upperelectrode 212, out of the charges generated in the organic photoelectricconversion film 211. In this case, in order to reset the FD unit 25 inwhich electrons are accumulated, the reset voltage V_(rst) at the timewhen the FD unit 25 is reset by the reset transistor 22 is set to thepower supply voltage V_(DD) (or a boosted voltage having a voltage valuehigher than the power supply voltage V_(DD)) as illustrated in FIG. 2B,

[Voltage Drop in FD Unit]

Here, the drop in the voltage (FD voltage) of the FD unit 25 will bedescribed. First, a case of a typical CMOS image sensor using aphotodiode as a photoelectric conversion unit will be described withreference to FIG. 3 . FIG. 3 is a timing waveform diagram illustrating atiming relationship of pixel drive of a typical CMOS image sensor.

In the timing waveform diagram of FIG. 3 , READ is a readout pulse fordriving a readout transistor (transfer transistor) that reads outcharges from the photodiode. Moreover, a signal after reset of the FDunit 25 is read out at time t₁₁, and a signal is read out at time t₁₂after the charge has been read out from the photodiode to the FD unit25.

In a typical CMOS image sensor, the FD unit 25 is in a floating statewhen the reset pulse RST transitions to an inactive state (low levelstate in this example) after the FD unit 25 is reset. Accordingly,feedthrough corresponding to the capacitive coupling lowers the voltageof the FD unit 25.

Furthermore, when the reset pulse RST is returned to the inactive state,charge injection, that is, a phenomenon in which electrons existing in achannel of the reset transistor 22 are injected into the FD unit 25 alsooccurs, and this phenomenon lowers the FD voltage in a similar manner.In the timing waveform diagram of FIG. 3 , (A) indicates a state inwhich the FD voltage drops due to the influence of the feedthrough ofthe reset pulse RST and the charge injection in the reset transistor 22.Drop of the FD voltage would deteriorate readout of electrons from thephotodiode.

As described above, in a typical CMOS image sensor, only the feedthroughof the reset pulse RST and the charge injection in the reset transistor22 have influence of the voltage drop after the FD unit 25 is reset.Furthermore, in a typical CMOS image sensor, since the signal chargestays in the FD unit 25 for several p seconds and thus, the FD unit 25is not easily influenced by electric field dark current such as junctionleakage. From the viewpoint of dark current, adjusting the FD voltageafter feedthrough and charge injection so as to be a certain voltage hasno high requirement.

Next, a voltage drop in the FD unit 25 in a case where the chargeaccumulation unit cannot be depleted, for example, in the case of thepixel configuration illustrated in FIGS. 2A and 2B in which charges areaccumulated in the FD unit 25 by using the organic photoelectricconversion film 211 in the photoelectric conversion unit 21 will bedescribed with reference to FIG. 4 . FIG. 4 is a timing waveform diagramillustrating a timing relationship of pixel drive in the case ofaccumulating charges in the FD unit 25 by using the organicphotoelectric conversion film 211 in the photoelectric conversion unit21.

With the configuration in which the signal charge is accumulated in theFD unit 25 by using the organic photoelectric conversion film 211 in thephotoelectric conversion unit 21, the dark current of the FD unit 25 isalso accumulated together with accumulation of the signal charge, andtherefore, there is a need to weaken the electric field of the FD unit25 in particular. One way to weaken the electric field of the FD unit 25is to reset the FD unit at the ground (GND) level as illustrated in FIG.2A so as to turn the accumulated charge to a hole. This makes itpossible to weaken the electric field of the FD unit 25 particularly inthe dark time.

However, the feedthrough of the reset pulse RST and the charge injectionin the reset transistor 22 lowers the FD voltage from the GND level andthis generates an electric field, leading to an increase in the darkcurrent of the FD unit 25. Furthermore, in the configuration in whichthe signal charge is accumulated in the FD unit 25 by using the organicphotoelectric conversion film 211, the time interval (t₂₂-t₂₁ interval)of the CDS processing of the signals before and after the chargeaccumulation becomes equal to the accumulation time of the signal, asillustrated in the timing waveform diagram of FIG. 4 .

Here, the time t₂₁ is a timing of reading out the signal (reset level)after the FD unit 25 is reset, while the time t₂₂ is a timing of readingout the signal (signal level) after the charges accumulated in the FDunit 25 are read out. Furthermore, the CDS processing is processing ofcapturing the reset level and the signal level output from the pixel 20and taking a difference between these levels and thereby removing thereset noise of the pixel 20 (noise removal processing)

In this manner, in the case of using a configuration in which the signalcharge is accumulated in the FD unit 25 by using the organicphotoelectric conversion film 211, the time interval of the CDSprocessing is equal to the accumulation time of the signal. Accordingly,the selection pulse SEL is set in an inactive state (low level state inthis example) after the reset level before accumulation is read out, andthen goes into a long accumulation phase (accumulation period) asillustrated in the timing waveform diagram of FIG. 4 .

With this arrangement, with a configuration in which the signal chargeis accumulated in the FD unit 25 by using the organic photoelectricconversion film 211, the feedthrough by the selection pulse SEL wouldhave an influence in addition to the feedthrough by the reset pulse RSTand the channel charge injection in the reset transistor 22. Since bothof them would lower the FD voltage, the influence of the dark current ofthe FD unit 25 would be more serious.

In the timing waveform diagram of FIG. 4 , (A) illustrates a state wherethe FD voltage drops due to the influence of the feedthrough of thereset pulse RST and the charge injection in the reset transistor 22.Furthermore, (B) illustrates a state where the FD voltage further dropsdue to the influence of the feedthrough caused by the selection pulseSEL. In order to avoid the influence of these, it is conceivable toadjust the voltage value of the reset voltage V_(rst) in considerationof the feedthrough amount. However, it is necessary to consider theinfluence of an increase in cost and power consumption to be caused byan increase in bias voltage and the number of power supply units, forexample.

<Embodiment of Present Disclosure>

Therefore, in the embodiment of the present disclosure, an effect ofboosting the FD voltage is to be positively utilized against the problemof the FD voltage drop after the time point when the selection pulse SELturns to the inactive state. Specifically, second wiring is formed alongthe first wiring in the vicinity of the first wiring electricallyconnecting the FD unit 25 being a charge accumulation unit and the gateelectrode of the amplification transistor 23. Subsequently, the secondwiring is electrically connected to a common connection node of theamplification transistor 23 and the selection transistor 24 (connectionpart between the source of the amplification transistor 23 and the drainof the selection transistor 24).

Furthermore, the amplification transistor 23 and the selectiontransistor 24 are electrically connected to each other by third wiring.More specifically, a source region (diffusion layer) of theamplification transistor 23 and a drain region (diffusion layer) of theselection transistor 24 are separated from each other, and then, thethird wiring is used to electrically connect the source region of theamplification transistor 23 and the drain region of the selectiontransistor 24. Each of the first wiring, the second wiring, and thethird wiring includes metal wiring.

In the pixel circuit illustrated in FIG. 5A (same as the pixel circuitin FIG. 2A), (1) to (3) indicate factors for lowering the FD voltage.Specifically, (1) indicates feedthrough by the reset pulse RST, (2)indicates channel charge injection in the reset transistor 22, and (3)indicates feedthrough by the selection pulse SEL. N is a commonconnection node of the amplification transistor 23 and the selectiontransistor 24. Hereinafter, the common node will be simply described asthe “node N” in some cases.

Now, as illustrated in the timing waveform diagram of FIG. 5B, when thereset pulse RST transitions to the inactive state after the FD unit 25is reset, the FD voltage drops due to the influence of the feedthrough(1) by the reset pulse RST and the channel charge injection (2) in thereset transistor 22. Furthermore, after the reset level is read out, theFD voltage further drops due to the influence of the feedthrough (3) bythe selection pulse SEL when the selection pulse SEL transitions to theinactive state and goes into the accumulation phase (accumulationperiod).

To avoid this, the embodiment of the present disclosure has aconfiguration in which the second wiring connected to the node N isprovided in the vicinity of and along the first wiring (FD wiring)connecting the FD unit 25 with the gate electrode of the amplificationtransistor 23. With this configuration, the capacitive coupling throughthe parasitic capacitance between the first wiring and the second wiringcan be increased. Accordingly, it is possible to cause the capacitancecoupling to boost the FD voltage that has dropped by factors (1) to (3)and to adjust the FD voltage to an appropriate value.

More specifically, in the pixel circuit illustrated in FIG. 5A, thereare effects of the boosting effect (4) by the capacitive coupling afterthe transition of the selection pulse SEL to the inactive state and theboosting effect (5) obtained by the channel of the amplificationtransistor 23 after the transition to the inactive state, and because ofthese effects, it is possible to boost the FD voltage and adjust it toan appropriate value. Moreover, capability of adjusting the FD voltageto an appropriate value would lead to execution of satisfactory readoutof the charge from the photoelectric conversion unit 21, enablingenhancement of the image quality of the captured image.

Furthermore, since the amplification transistor 23 and the selectiontransistor 24 are connected to each other by the third wiring ratherthan connected by a shared diffusion layer, it is possible to improvethe degree of freedom of arrangement of the selection transistor 24,making it possible to arrange the selection transistor 24 at a positiondistant from the FD unit 25. With this configuration, it is possible tosuppress the FD voltage drop due to the influence of the feedthrough (3)by the selection pulse SEL, as compared with the case where thediffusion layer is shared.

Here, boosting of the FD voltage by the boosting effects (4) and (5)will be described in more detail. In an active period of the selectionpulse SEL (high level state in this example), a path from the othersource/drain electrode (source electrode in this example) of theamplification transistor 23 through the selection transistor 24 to thevertical signal line 17 is biased as an output of the source followerwith the FD voltage as an input. Therefore, the voltage of the commonconnection node of the amplification transistor 23 and the selectiontransistor 24, that is, the voltage of the node N is lower than thepower supply voltage V_(DD).

Thereafter, when the selection pulse SEL transitions from the activestate to the inactive state, electrons in the channel of theamplification transistor 23 and the electrons at the node N escape tothe power supply voltage V_(DD) side, causing an increase in the voltageat the node N. The effect (4) of the escape of the electrons in thechannel of the amplification transistor 23 to the power supply voltageV_(DD) side can be used to boost the FD voltage by capacitive couplingof a gate oxide film of the amplification transistor 23.

Furthermore, since the capacitive coupling with the FD unit 25 can bestrengthened by connecting the amplification transistor 23 and theselection transistor 24 with metal wiring being the third wiring, or bydrawing out the metal wiring, it is possible to obtain high degree offreedom of design. Furthermore, increasing the capacitance of the FDunit 25 would normally decrease the charge-voltage conversion efficiencyat the FD unit 25. However, the node N is the output node of the sourcefollower, and its capacitance is as small as (1-α) times due to theMiller effect. Here, α is the gain of the source follower. Furthermore,the portion coupled with the other node can be coupled to the node N,making it possible to obtain shielding effects of reducing the totalcapacity, leading also to charge-voltage conversion efficiency in the FDunit 25.

The above effects would be particularly effective for the solid-stateimaging element 10 illustrated in FIG. 2A, that accumulates charges(holes) in the FD unit 25 and reset the FD unit 25 at the GND level. Inaddition, even in a case where charge accumulation is not performed inthe FD unit 25 and the boosting effect at the time of transition of theselection pulse SEL to the inactive state cannot be obtained as in atypical CMOS image sensor, effects of obtaining enhanced charge-voltageconversion efficiency in the FD unit 25 are still expected. Accordingly,this can be defined as an effective means for solid-state imagingelements in general.

Hereinafter, specific examples of the wiring structure of the firstwiring, the second wiring, and the third wiring will be described.

EXAMPLE 1

Example 1 is an example of arranging the first wiring and the secondwiring stacked on different layers. FIG. 6A is a plan view of a wiringstructure according to Example 1, and FIG. 6B is a cross-sectional viewtaken along line A-A of FIG. 6A. Here, while an exemplary case of apixel circuit illustrated in FIG. 2A in which the reset voltage V_(rst)of the FD unit 25 is set to the GND level is illustrated, the pixelcircuit illustrated in FIG. 2B in which the reset voltage V_(rst) is setto the power supply voltage V_(DD) has basically the similar wiringstructure. This similarly applies to Examples to be described in thefollowing.

In the reset transistor 22, one diffusion layer (source/drain region) 22⁻¹ side is the FD unit 25 and the other diffusion layer (source/drainregion) 22 ⁻² is provided with the GND level via a contact part 41. Inthe case of the pixel circuit illustrated in FIG. 2B, the power supplyvoltage V_(DD) is applied to the other diffusion layer 22 ⁻². Meanwhile,one end of a first wiring 31 is electrically connected to one diffusionlayer 22 ⁻¹ on the FD unit 25 side via a contact part 42.

The first wiring 31 is formed in the first wiring layer, for example,with the other end electrically connected to a gate electrode 23 _(G) ofthe amplification transistor 23 via a contact part 43. The gateelectrode 23 _(G) of the amplification transistor 23 is formed on thesemiconductor substrate 51 via a gate oxide film 52.

In the amplification transistor 23, the power supply voltage V_(DD) isapplied to one diffusion layer (source/drain region) 23 ⁻¹ via a contactpart 44. Meanwhile, one end of a second wiring 32 is electricallyconnected to the other diffusion layer (source/drain region) 23 ⁻² via acontact part 45. The second wiring 32 is formed in an L shape in a planview in the second wiring layer, for example, such that the other endside of the second wiring 32 extends along the first wiring 31.Moreover, one end of a third wiring 33 is electrically connected to theother diffusion layer 23 ⁻² of the amplification transistor 23 via thecontact part 45.

The third wiring 33 is formed in the first wiring layer, for example,with the other end electrically connected to one diffusion layer(source/drain region) 24 ⁻¹ of the selection transistor 24 via a contactpart 46. That is, the amplification transistor 23 and the selectiontransistor 24 are electrically connected by the third wiring 33, ratherthan by sharing the diffusion layer 23 ⁻² and the diffusion layer 24 ⁻¹.The other diffusion layer (source/drain region) 24 ⁻² of the selectiontransistor 24 is electrically connected to the vertical signal line 17via a contact part 47.

In order to clarify the difference of wiring in the pixel structureillustrated in FIG. 6A, the first wirings 31 and the third wiring 33being wiring of the first layer are indicated by one-dot chain lines,while the second wiring 32 being wiring in the second layer and thesignal line 17 are illustrated by solid lines.

As described above, the wiring structure according to Example 1 is awiring structure in which the second wiring 32 connected to the otherdiffusion layer 23 ⁻² of the amplification transistor 23 is stacked andformed along the first wiring 31 that connects the FD unit 25 and thegate electrode 23 _(G) of the amplification transistor 23, in differentwiring layers. With this configuration, capacitive coupling through theparasitic capacitance between the first wiring 31 and the second wiring31 can be increased, making it possible to boost the FD voltage by thecapacitive coupling.

Furthermore, there is provided a wiring structure that connects theamplification transistor 23 and the selection transistor 24 by using thethird wiring 31 rather than connecting by sharing the diffusion layers(the diffusion layer 23 ⁻² and the diffusion layer 24 ⁻¹). Thisstructure increases the degree of freedom of the layout of the selectiontransistor 24 and allows the selection transistor 24 to be arranged at aposition distant from the FD unit 25, making it possible to suppress thevoltage drop of the FD unit 25 due to the influence of feedthroughcaused by the selection pulse SEL.

EXAMPLE 2

Example 2 is an example in which the first wiring and the second wiringare arranged in parallel in a same layer. FIG. 7A is a plan view of thewiring structure according to Example 2, and FIG. 7B is across-sectional view taken along line B-B of FIG. 7A.

According to the wiring structure of Example 2, both the second wiring32 and the third wiring 33 are formed in the same first wiring layer asthe first wiring 31. Specifically, the first wiring 31 is formed in thefirst wiring layer, one end of which being electrically connected to theFD unit 25 via the contact part 42, while the other end is electricallyconnected to the gate electrode 23 _(G) of the amplification transistor23 via the contact part 43.

The second wiring 32 is formed in parallel with the first wiring 31 inthe first wiring layer, with one end of the second wiring 32 beingelectrically connected to the other diffusion layer 23 ⁻² of theamplification transistor 23 via the contact part 45. Furthermore, thethird wiring 33 is formed in the first wiring layer, while the other endis electrically connected to one diffusion layer 24 ⁻¹ of the selectiontransistor 24 via the contact part 46. In order to clarify thedifference of wiring in the pixel structure illustrated in FIG. 7A, thefirst wiring 31, the second wiring 32, and the third wiring 33 being thefirst layer wiring are illustrated by one-dot chain lines, while thesignal line 17 being the second layer wiring is illustrated by solidlines.

As described above, the wiring structure according to Example 2 is awiring structure in which the second wiring 32 connected to the otherdiffusion layer 23 ⁻² of the amplification transistor 23 is formed inparallel along the first wiring 31 that connects the FD unit 25 and thegate electrode 23 _(G) of the amplification transistor 23, in a samewiring layer. In the case of this wiring structure, the first wiring 31and the second wiring 32 are opposed to each other on the side surface.This makes it possible to boost the FD voltage by capacitive couplingthrough parasitic capacitance, although the parasitic capacitancebetween the first wiring 31 and the second wiring 31 is slightly reducedcompared with the wiring structure according to Example 1 in which thefirst wiring 31 and the second wiring 32 are opposed with upper/lowersurfaces.

EXAMPLE 3

Example 3 is a modification of Example 1. This is an example in whichthe first wiring and the second wiring are arranged in parallel indifferent layers. FIG. 8A is a plan view of the wiring structureaccording to Example 3, and FIG. 8B is a cross-sectional view takenalong line C-C of FIG. 8A.

The wiring structure according to Example 1 is a wiring structure inwhich the first wiring 31 and the second wiring 32 are verticallystacked in different wiring layers. In contrast, the wiring structureaccording to Example 3 is a wiring structure in which the first wiring31 and the second wiring 32 are formed in parallel in different wiringlayers, in other words, formed in a positional relationship beingadjacent to each other in parallel in the diagonal direction.

Specifically, the first wiring 31 is formed in the first wiring layer,one end of which being electrically connected to the FD unit 25 via thecontact part 42, while the other end is electrically connected to thegate electrode 23 _(G) of the amplification transistor 23 via thecontact part 43. The second wiring 32 is formed in parallel with thefirst wiring 31 in the second wiring layer, with one end of the secondwiring 32 being electrically connected to the other diffusion layer 23⁻² of the amplification transistor 23 via the contact part 45.Furthermore, the third wiring 33 is formed in the first wiring layer,while the other end is electrically connected to one diffusion layer 24⁻¹ of the selection transistor 24 via the contact part 46.

As described above, the wiring structure according to Example 3 is awiring structure in which the first wiring 31 and the second wiring 32are adjacent to each other in the diagonal direction in different wiringlayers and are arranged in parallel along the first wiring 31. In thecase of this wiring structure, the first wiring 31 and the second wiring32 are adjacent to each other in the diagonal direction. This makes itpossible to boost the FD voltage by capacitive coupling throughparasitic capacitance, although the parasitic capacitance between thefirst wiring 31 and the second wiring 31 is slightly reduced comparedwith the wiring structure according to Example 1 in which the firstwiring 31 and the second wiring 32 are opposed with upper/lowersurfaces.

Note that, in the wiring structures according to Examples 1 to 3, thefirst wiring 31, the second wiring 32, and the third wiring 33 may beformed by metal wiring including copper (Cu), aluminum (Al), or thelike.

EXAMPLE 4

Example 4 is an example of wiring materials of the first wiring 31, thesecond wiring 32, and the third wiring 33. While Examples 1 to 3 use thesame wiring material as the first wiring 31, the second wiring 32, andthe third wiring 33, it is allowable to use mutually different wiringmaterials. For example, in the wiring structure of Example 1, it ispossible to use tungsten (W) as the wiring material of the first wiring31, for example, and possible to use copper, aluminum, or the like, asthe wiring material of the second wiring 32 and the third wiring 33.Conversely, it is possible to use copper, aluminum, or the like, as thewiring material of the first wiring 31 and possible to use tungsten (W)as the wiring material of the second wiring 32 and the third wiring 33,for example. Furthermore, the wiring material of the second wiring 32and the third wiring 33 need not be the same, and can be mutuallydifferent wiring materials.

<Vertical Spectroscopic Pixel Structure>

There is a solid-state imaging element having a vertical spectroscopicpixel structure. This structure includes a photoelectric conversion filmthat performs photoelectric conversion on light in a predeterminedwavelength zone provided outside a semiconductor substrate whileincluding, inside the semiconductor substrate, at least twophotoelectric conversion regions that perform photoelectric conversionon light in a wavelength region other than the predetermined wavelengthzone having passed through the photoelectric conversion film.

According to the vertical spectroscopic pixel structure, it is possibleto arrange photoelectric conversion units (photoelectric conversionfilms and photoelectric conversion regions) having sensitivity for twoor more colors in the one pixel region. This is advantageous inenhancing light use efficiency compared with a case of disposing aphotoelectric conversion unit having sensitivity for two or more colorsin a planar manner. The technology of the present disclosure can also beapplied to a solid-state imaging element having the verticalspectroscopic pixel structure.

The vertical spectroscopic pixel structure will be described withreference to FIG. 9 . FIG. 9 illustrates a vertical spectroscopic pixelstructure.

In FIG. 9 , a semiconductor region 63 and a semiconductor region 64 ofthe second conductivity type (for example, N type) are stacked andformed in a semiconductor region 62 of the first conductivity type (forexample, P type) of the semiconductor substrate 61 in a substrate depthdirection. This leads to formation of a photodiode PD₁ and a photodiodePD₂ by PN junction in a stacked state in the substrate depth direction.The photodiode PD₁ having the semiconductor region 63 as a chargeaccumulation region is an inorganic photoelectric conversion unit thatreceives blue light and performs photoelectric conversion, for example.The photodiode PD₂ having the semiconductor region 64 as a chargeaccumulation region is an inorganic photoelectric conversion unit thatreceives red light and performs photoelectric conversion, for example.

The front side (lower side in the drawing) of the semiconductorsubstrate 61 includes a multilayer wiring layer 65. The multilayerwiring layer 65 includes: a plurality of pixel transistors that performsreadout, or the like, of the charges photoelectrically converted by thephotodiode PD₁ and the photodiode PD₂ and accumulated; a plurality ofwiring layers; and an interlayer insulation film. Note that FIG. 9 omitsdetailed illustration of the multilayer wiring layer 65.

The semiconductor substrate 61 includes a conductive plug 67 forextracting charges photoelectrically converted by an organicphotoelectric conversion film 66 (corresponding to the organicphotoelectric conversion film 211 in FIGS. 2A and 2B) described later,to the multilayer wiring layer 65 side. This conductive plug 67 isformed to penetrate the semiconductor region 62 within the semiconductorsubstrate 61. An outer periphery of the conductive plug 67 includes aninsulation film 47 including SiO₂ or SiN provided in order to suppress ashort circuit with the semiconductor region 62.

The conductive plug 67 is electrically connected to a floating diffusionunit 70 formed of a semiconductor region of the second conductivity type(for example, N type) in the semiconductor substrate 61 via metal wiring69 formed in the multilayer wiring layer 65. The floating diffusion unit70 is a charge voltage conversion unit that temporarily holds the chargephotoelectrically converted by the organic photoelectric conversion film52 and that converts the charge into a voltage.

An interface of the back side of the semiconductor substrate 61 (on theupper side/the side opposite to the side on which the multilayer wiringlayer 65 is formed) includes a transparent insulating film 71 includinga two-layer or three-layer film of a hafnium oxide (HfO₂) film and asilicon oxide film.

On the upper side of the transparent insulating film 71, the organicphotoelectric conversion film 66 is sandwiched between a lower electrode72 (corresponding to the lower electrode 213 in FIGS. 2A and 2B) and anupper electrode 73 (corresponding to the upper electrode 212 in FIGS. 2Aand 2B). The organic photoelectric conversion film 66, the lowerelectrode 72, and the upper electrode 73 constitute an organicphotoelectric conversion unit. The organic photoelectric conversion film66 includes, for example, when used as a film that performsphotoelectric conversion of light of green wavelength, organicphotoelectric conversion materials including rhodamine-based pigments,merocyanine-based pigments, quinacridone, and the like, for example. Thelower electrode 72 and the upper electrode 73 are formed of an indiumtin oxide (ITO) film, an indium zinc oxide film, for example.

Note that in a case where the organic photoelectric conversion film 66is used as a film that performs photoelectric conversion of redwavelength light, it is possible to use organic photoelectric conversionmaterials including phthalocyanine-based pigments, for example.Moreover, in a case where the organic photoelectric conversion film 66is used as a film that performs photoelectric conversion of bluewavelength light, it is possible to use organic photoelectric conversionmaterials including coumarin-based pigments, tris-8-hydroxyquinoline-Al(Alq3), merocyanine-based pigments, and the like.

The upper electrode 73 is formed over the entire surface in common forall the pixels. In contrast, the lower electrode 72 is formed in pixelunits, and is electrically connected to the conductive plug 67 of thesemiconductor substrate 61 by the metal wiring 74 penetrating thetransparent insulating film 71. The metal wiring 74 is formed of amaterial such as tungsten (W), aluminum (Al), and copper (Cu). The metalwiring 74 is also formed in a planar direction at a predetermined depthof the transparent insulating film 71 and also serves as an inter-pixellight shielding film 75 that suppresses incidence of light to adjacentpixels.

On an upper surface of the upper electrode 73, a high refractive indexlayer 76 is formed with an inorganic membrane including silicon nitridefilm (SiN), silicon oxynitride film (SiON), silicon carbide (SiC), orthe like. Furthermore, an on-chip lens 77 is formed on the highrefractive index layer 76. Examples of materials of the on-chip lens 77include a silicon nitride film (SiN), or resin-based materials such asstyrenic resin, acrylic resin, styrene-acrylic copolymer resin, orsiloxane based resin. Since the present pixel structure has a shortdistance between the organic photoelectric conversion film 66 and theon-chip lens 77, interposing the high refractive index layer 76 wouldincrease the refraction angle, leading to enhancement of the condensingefficiency.

As described above, the pixel structure according to the presentconfiguration example is a back-illuminated pixel structure which lightenters from the back side, that is, an opposite side of the multilayerwiring layer 65 side, defined as a front side of the semiconductorsubstrate 61, on which pixel transistors, wiring, and the like, areformed. Furthermore, the pixel structure is a vertical spectroscopicpixel structure that performs, for example, photoelectric conversion onthe green light by the organic photoelectric conversion film 66 formedabove the semiconductor substrate 61, and that performs photoelectricconversion on blue and red light by the photodiode PD1 and thephotodiode PD2 within the semiconductor substrate 61.

<Electronic Device of the Present Disclosure>

The solid-state imaging element according to the embodiments describedabove is applicable as an imaging unit (image capture unit) in animaging apparatus such as a digital still camera or a video camera, amobile terminal apparatus having an imaging function such as a cellularphone, or in general electronic devices such as a copier using asolid-state imaging element in an image reading part. Note that thesolid-state imaging element may be formed as a one-chip device, or maybe provided in a module form having an imaging function as a packagecollectively including an imaging unit and a signal processing unit oran optical system. The module form mounted on the electronic device,that is, a camera module may be the imaging apparatus in some cases.

[Imaging Apparatus]

FIG. 10 is a block diagram illustrating a configuration of an imagingapparatus as an example of the electronic device of the presentdisclosure. As illustrated in FIG. 10 , an imaging apparatus 100according to the present example includes an imaging optical system 101including a lens group, etc., an imaging unit 102, a DSP circuit 103, aframe memory 104, a display apparatus 105, a recording apparatus 106, anoperation system 107, a power supply system 108, and the like. Amongthese, the DSP circuit 103, the frame memory 104, the display apparatus105, the recording apparatus 106, the operation system 107, and thepower supply system 108 are mutually connected via a bus line 109.

The imaging optical system 101 captures incident light (image light)from a subject and forms an image on an imaging surface of the imagingunit 102. The imaging unit 102 converts the light amount of the incidentlight imaged on the imaging surface by the optical system 101 intoelectric signals in pixel units and outputs the electric signals aspixel signals. The DSP circuit 103 performs general camera signalprocessing such as white balance processing and gamma correctionprocessing, for example.

The frame memory 104 is used for storing data as appropriate during thesignal processing in the DSP circuit 103. The display apparatus 105 is apanel type display apparatus such as a liquid crystal display apparatusor an organic electro luminescence (EL) display apparatus, and displaysmoving images or still images captured by the imaging unit 102. Therecording apparatus 106 records the moving image or the still imagecaptured by the imaging unit 102 on a recording medium such as aportable semiconductor memory, an optical disc, or hard disk drive(HDD).

The operation system 107 issues an operation command for variousfunctions provided in the imaging apparatus 100 under the operation ofthe user. The power supply system 108 appropriately provides varioustypes of power supply serving as operating power supply to the DSPcircuit 103, the frame memory 104, the display apparatus 105, therecording apparatus 106, and the operation system 107 to these supplytargets.

In the imaging apparatus 100 having the above configuration, thesolid-state imaging element according to the above-described embodimentcan be used as the imaging unit 102. The solid-state imaging elementaccording to the above-described embodiment can adjust the FD voltage toan appropriate value, leading to execution of satisfactory readout ofthe charge from the photoelectric conversion unit, enabling enhancementof the image quality of the captured image. Therefore, with the use ofthe solid-state imaging element according to the above-describedembodiment as the imaging unit 102, it is possible to capture an imagewith high image quality.

<Configuration Achievable by the Present Disclosure>

Note that the present disclosure can also be configured as follows.

[1] A solid-state imaging element having arranged inside a pixel:

-   a charge accumulation unit that accumulates a charge    photoelectrically converted by a photoelectric conversion unit;-   a reset transistor that selectively applies a reset voltage to the    charge accumulation unit;-   an amplification transistor having a gate electrode being    electrically connected to the charge accumulation unit; and-   a selection transistor connected in series to the amplification    transistor,-   the solid-state imaging element including:-   first wiring electrically connecting the charge accumulation unit    and the gate electrode of the amplification transistor;-   second wiring electrically connected to a common connection node of    the amplification transistor and the selection transistor and formed    along the first wiring; and-   third wiring electrically connecting the amplification transistor    and the selection transistor.

[2] The solid-state imaging element according to [1],

-   in which, when the charge accumulation unit accumulates holes, the    reset voltage is at a GND level.-   [3] The solid-state imaging element according to [1],-   in which, when the charge accumulation unit accumulates electrons,    the reset voltage is a power supply voltage or a boosted voltage    having a voltage value higher than the power supply voltage.-   [4] The solid-state imaging element according to any of [1] to [3],-   in which the first wiring and the second wiring are formed in    parallel in different wiring layers.-   [5] The solid-state imaging element according to any of [1] to [3],-   in which the first wiring and the second wiring are formed in    parallel in a same wiring layer.-   [6] The solid-state imaging element according to any of [1] to [5],-   in which wiring of any one of the first wiring, the second wiring,    and the third wiring includes a wiring material different from the    material of the other wiring.

[7] The solid-state imaging element according to any of [1] to [6],

-   in which the photoelectric conversion unit includes an organic    photoelectric conversion film.

[8] The solid-state imaging element according to any of [1] to [7],

-   in which at least two photoelectric conversion regions are stacked    in a light incident direction in a semiconductor substrate on which    pixels are formed.

[9] The solid-state imaging element according to any of [1] to [8],

-   in which the pixel has a back-illuminated pixel structure.

[10] An electronic device including a solid-state imaging element havingarranged inside a pixel:

-   a charge accumulation unit that accumulates a charge    photoelectrically converted by a photoelectric conversion unit;-   a reset transistor that selectively applies a reset voltage to the    charge accumulation unit;-   an amplification transistor having a gate electrode being    electrically connected to the charge accumulation unit; and-   a selection transistor connected in series to the amplification    transistor,-   the solid-state imaging element including:-   first wiring electrically connecting the charge accumulation unit    and the gate electrode of the amplification transistor;-   second wiring electrically connected to a common connection node of    the amplification transistor and the selection transistor and formed    along the first wiring; and-   third wiring electrically connecting the amplification transistor    and the selection transistor.

REFERENCE SIGNS LIST

-   10 Solid-state imaging element-   11 Pixel array unit-   12 Vertical drive unit-   13 Column processing unit-   14 Vertical drive unit-   15 System control unit-   16(16 ₁ to 16 _(m))Pixel drive line-   17(17 ₁ to 17 _(n))Vertical signal line-   18 Signal processing unit-   19 Data storage unit-   20 Pixel (unit pixel)-   21 Photoelectric conversion unit-   22 Reset transistor-   23 Amplification transistor-   24 Selection transistor-   25 Floating diffusion unit (FD unit)-   26 Bias power supply-   31 First wiring-   32 Second wiring-   33 Third wiring

1. A solid-state imaging element having arranged inside a pixel: acharge accumulation unit that accumulates a charge photoelectricallyconverted by a photoelectric conversion unit; a reset transistor thatselectively applies a reset voltage to the charge accumulation unit; anamplification transistor having a gate electrode being electricallyconnected to the charge accumulation unit; and a selection transistorconnected in series to the amplification transistor, the solid-stateimaging element comprising: first wiring electrically connecting thecharge accumulation unit and the gate electrode of the amplificationtransistor; second wiring electrically connected to a common connectionnode of the amplification transistor and the selection transistor andformed along the first wiring; and third wiring electrically connectingthe amplification transistor and the selection transistor.
 2. Thesolid-state imaging element according to claim 1, wherein, when thecharge accumulation unit accumulates holes, the reset voltage is at aGND level.
 3. The solid-state imaging element according to claim 1,wherein, when the charge accumulation unit accumulates electrons, thereset voltage is a power supply voltage or a boosted voltage having avoltage value higher than the power supply voltage.
 4. The solid-stateimaging element according to claim 1, wherein the first wiring and thesecond wiring are formed in parallel in different wiring layers.
 5. Thesolid-state imaging element according to claim 1, wherein the firstwiring and the second wiring are formed in parallel in a same wiringlayer.
 6. The solid-state imaging element according to claim 1, whereinwiring of any one of the first wiring, the second wiring, and the thirdwiring includes a wiring material different from the material of theother wiring.
 7. The solid-state imaging element according to claim 1,wherein the photoelectric conversion unit includes an organicphotoelectric conversion film.
 8. The solid-state imaging elementaccording to claim 1, wherein at least two photoelectric conversionregions are stacked in a light incident direction in a semiconductorsubstrate on which pixels are formed.
 9. The solid-state imaging elementaccording to claim 1, wherein the pixel has a back-illuminated pixelstructure.
 10. An electronic device including a solid-state imagingelement having arranged inside a pixel: a charge accumulation unit thataccumulates a charge photoelectrically converted by a photoelectricconversion unit; a reset transistor that selectively applies a resetvoltage to the charge accumulation unit; an amplification transistorhaving a gate electrode being electrically connected to the chargeaccumulation unit; and a selection transistor connected in series to theamplification transistor, the solid-state imaging element comprising:first wiring electrically connecting the charge accumulation unit andthe gate electrode of the amplification transistor; second wiringelectrically connected to a common connection node of the amplificationtransistor and the selection transistor and formed along the firstwiring; and third wiring electrically connecting the amplificationtransistor and the selection transistor.